The present invention relates to a magnetic recording medium and a fabrication method therefor. More in detail it relates to an improvement of an in-plane magnetic recording medium suitable for high-density magnetic recording.
As a magnetic recording medium there is known a magnetic recording medium, in which a magnetic film is superposed on a non-magnetic substrate through an underlayer. A Co alloy is used for the magnetic film. The crystallographic structure of this Co alloy is a hexagonal close packed structure (hereinbelow abbreviated to h.c.p.) similarly to Co of simple substance, which has an easy magnetization axis in the direction of c-axis, i.e. [0001] axis. Consequently, in case where the Co alloy described above is used for the magnetic film for a high-density magnetic recording medium, it is necessary to direct the easy magnetization axis, i.e. c-axis, substantially in the plane of the magnetic film. That is, it is necessary that the easy magnetization axis is parallel to the direction, in which the magnetic film extends.
In order that the easy magnetization axis is oriented parallelly to the magnetic film, there is known a method, by which an underlayer having a body centered cubic structure (hereinbelow abbreviated to b.c.c.) is disposed below the magnetic film. When this underlayer has a &lt;100&gt; orientation, the orientation of the magnetic film dispose thereon is &lt;1120&gt; and in this way the easy magnetization axis is oriented parallelly to the magnetic film. Concretely speaking, a construction of a high-density magnetic recording medium usable in practice at present is formed by superposing a Cr based metal layer on an Al substrate, whose surface is covered by an NiP layer, by a well-known method as an underlayer and then by superposing a Co based magnetic film further thereon by a well-known method. In such a construction, since the underlayer has a substantially &lt;100&gt; orientation, the Co based magnetic film disposed thereon has a &lt;1120&gt; orientation and thus the easy magnetization axis is parallel to the surface of the magnetic film.
U.S. Pat. No. 4,654,276, U.S. Pat. No. 4,652,499, U.S. Pat. No. 4,789,598 and U.S. Pat. No. 5,063,120 can be cited as literatures showing magnetic recording media having such a construction and these literatures are incorporated herein by reference.
However, since the Al substrate is soft, it may be deformed, when a strong impact is applied thereto from the exterior. Further, although it is required to smoothen further the surface of the substrate with recent increasing magnetic recording density and decreasing size of apparatus, softness of the substrate imposes a restriction thereon, when the surface thereof is polished so as to be smooth.
Therefore it is conceived to form the substrate by using a hard and non-magnetic material such as glass and a magnetic recording medium provided with a glass substrate is disclosed e.g. in literatures described below:
Literature: J. Appl. Phys. 67(9), 1 May (1990), pp. 4913-4915 and PA1 Literature: JP-A-Sho 63-106917. This publication discloses a medium so constructed that an underlayer made of Cr, Mo, Ti or Ta having a predetermined thickness is disposed on a glass substrate and a magnetic film made of Co, Ni, Cr and Pt, in which the content of Pt is 1 to 43 atom %, is formed further thereon.
However, as far as the inventors know, such a magnetic recording medium provided with a glass substrate is inferior in magnetic characteristics to that having an Al/NiP substrate described previously and therefore it was not practical as a high-density magnetic recording medium.